Well-treating apparatus



B. SILVER 3,270,668

Sept 6, 1966 34 35 Ma 24 5/ 52 l3 g INVENTOR /0 BERNARD SILVER ATTORNEYUnited States Patent O 3,270,668 WELL-TREATING APPARATUS Bernard Silver,Alexandria, Va., assignor to Atlantic Research Corporation, FairfaxCounty, Va., a corporation of Virginia Filed Dec. 29, 1964, Ser. No.421,896 Claims. (Cl. 102-20) This invention relates to well-treatingapparatus and, more particularly, to means for generating high-pressuregas and high flow rate for improving oil, gas or water recovery.

In the art of oil, gas and water recovery, it is a common problem forthe quantum of recovery to be reduced considerabyl due to the presenceof sedimentation, petroleum wax, or other foreign matter. It is alsonecessary to provide fissures or cracks in the earth formation tioninorder to effect flow of the desired recoverable substance into the wellfrom which it can be extracted. Several methods have been employed inthe past to overcome these obstacles, however, each of these methods hasdistinct disadvantages which are overcome by the subject invention.

The most common fracturing and cleaning method employs a liquid underpressure, this being known as hydrofracting. Hydrofracting requiressupplying large quantities of water under high pressure down the welland into the earth formation. Attaining the high pressures and/or highinjection rates required necessitates the use of expensive and large,relatively non-portable equipment as well as the availability of severalthousand gallons of water. The fracturing fluid must be pumped down thewell in tubing and applied at the desired depth through perforations inthe well tubing or through the bottom of the tubing which results inhighfriction loss with concomitant reductions in injection rates andpressures and often results in failure to fracture or in inadequatefracturing or cleaning.

Another common and well-established method is the use of an explosive,such as nitroglycerin; however, in order to avoid fracture anddestruction of the well tubing, it is necessary to raise the tubingabove the level at whihc the explosive is to be detonated. This processis time-consuming and expensive. Furthermore, the need to maintainnitroglycerin or other explosives in the field provides logisticsproblems due to the dangerous nature of the explosives.

A third method which has been recently adopted is the use of containersof pressurized carbon dioxide, the containers having a heating elementtherein and a burst diaphra-gm closing off one end of the container. Thecontainer is lowered into the well and the heating element is energizedcausing heating of the carbon dioxide and an increase in internalpressure. At a predetermined pressure, the burst diaphragm fails and thepressurized CO is expelled into the well. The results received with thismethod have been generally unsuccessful thus accounting for its limitedacceptance.

It can be seen, therefore, that there is a substantial need forWell-treating apparatus which effectively removes the foreign matter inthe earth formation preventing successful recovery of the desiredproduct (oil, gas, or water) and which can fracture the earth formationwhen desired. This apparatus should be easily portable, inexpensive,both in manufacturing and operation, and reliable.

Accordingly, it is one object of the present invention to provide awell-treating apparatus capable of reliably supplying a prescribed fluidpressure and flow rate at a desired depth in the well.

It is another object of the present invention to provide a well-treatingapparatus which is portable, inexpensive to manufacture, easy andinexpensive to operate, and relatively safe to use and store.

Further objects and attendant advantages of the present invention willbecome better understood from the following description and accompanyingdrawings.

Briefly stated, this invention in one form provides a neutral-thrust gasgenerator comprising a tubular cylindrical casing, a solid propellantgrain mounted within the casing, ignition means, and removable aperturedmeans secured at both ends of the casing. Additionally, a diaphragm isprovided to obturate the apertures at both ends of the casing in orderto prevent moisture and foreign particles from entering the interior ofthe gas generator. The diaphragm also assists in providing accuratemeans for permitting establishment of a predetermined pressure withinthe gas generator casing.

The gas generator is lowered into the well to the desired depth at whichtime the ignition means is energized to effect ignition of the solidpropellant grain. Burning of the grain rapidly produces gaseouscombustion products which are maintained within the casing by thediaphragms until a predetermined pressure is attained. Upon attainmentof the predetermined pressure, the diaphragms at both ends of the casingare ejected and the combustion products rapidly flow through bothapertured means into the well and the surrounding earth formation. Thegas generator can be reused by simply removing one or both aperturedmeans and reloading the casing.

In the accompanying drawings, in which identical parts are denoted bythe same reference numerals,

FIGURE 1 is a sectional view of a gas generator formed in accordancewith one embodiment of this invention.

FIGURES 2, 3, and 4 are sectional views of solid propellant grainsillustrating various internal surface configurations,

FIGURE 5 is a sectional view of one end of a gas generator formed inaccordance with a second embodiment of this invention,

FIGURE 6 is a sectional view of one end of a gas generator formed inaccordance with a third embodiment of this invention,

FIGURE 7 is a sectional view of one end of a gas generator formed inaccordance with a fourth embodiment of this invention,

FIGURE 8 is a sectional view of one end of a gas generator formed inaccordance with a fifth embodiment of this invention.

With reference to the drawings and, more particularly, FIGURE 1, thereis illustrated a gas generating welltreating apparatus 10 comprising atubular cylindrical casing 12 having a combustion section 13, a solidpropellant grain 14 mounted centrally within the combustion section 13,a pair of apertured means or inserts 16, 18, one being mounted at eachend of the casing 12, and diaphragms 20, 22, for obturating each of theinserts 16, 18, respectively. Ignition means 24 is located within thegrain 14 in order to ignite the grain upon command.

The casing 12 may be made of any suitable material which can withstandthe pressures and temperatures to which it will be subjected. Forexample, the casing is made preferably of steel or aluminum tubing,however, other materials such as glass fiber or reinforced plastics canalso be employed.

If the material used for the casing 12 so requires, and if theparticular burning rate of the grain makes it necessary, an insulatorliner 26 may be located between the grain 14 and the casing. The lineran be an independent member or molded directly on theouter surface ofthe grain 14. Examples of suitable insulator material arephenolicchamber, and the duration of gas generation.

impregnated asbestos, phenolic-impregnated paper and plastic-reinforcedcloth.

In order to fracture the earth formation it is necessary to supply highpressure fluid at a high flow rate. Consequently, it is necessary todesign the propellant grain 14 such that it burns rapidly thus producingthe desired pressure and flow rate. In addition, it is necessary to keepthe costs as low as possible. One type of grain that can produce thedesired result is the conventional internalburning grain such asillustrated in FIGURE 1. The particular configuration of the internalsurface is determined by the characteristics of the particularpropellant used and the desired performance requirements. Examples ofvarious internal configurations are the straight cylindrical grain 14ashown in FIGURE 1, the ruciform 14b shown in FIGURE 2, the star 140shown in FIGURE 3, and the wagon wheel 14d shown in FIGURE 4. These aremerely four examples of internal-burning grains and it is not intendedto imply that they are the only configurations that can be used.

The particular propellant formulation can be chosen from the manywell-known moldable, castable or extrudable formulations, for example,double-base, e.g., nitrocellulose plasticized with nitroglycerin orother nitrated liquid plasticizer; composite propellants comprising anorganic binder, e.g., polyvinyl chloride, polyurethane, polyether,polysulfide (Thiokol), polybutadiene acrylic acid, etc., and

an oxidizer, e.g., ammonium and alkali metal nitrates and perchlorate,metal peroxides, etc.

Because of the simplicity of grain design, the grain can be'manufacturedby any of the conventional propellant molding methods, however, thegrain is particularly adaptable to being manufactured by a continuousextrusion process' wherein agrain of continuous length is extruded andcut to the desired length. The finished grain 14 is thencartridge-loaded into the casing 12.

In order to restrict burning to the internal surface of the grains 14 apair of resilient annular inhibitor members 28, 30 are placed at theends of the grain and are held in a partially compressed state by theinserts 16, 18 as described below. The annular members 28, 30additionally serve as as seal between the grain 14 and the inserts andrestrict the flow of combustion products to an axial direction thuspreventing the flow of the combustion products across the ends of thegrain and around the outer surface thereof. The annular members 28, 30can be fabricated from any heat-resistant resilient material. Selectionof a particular material depends upon many factors such as the environ-.mental temperatures in which the gas generator will be stored, theoperating temperature within the combustion Because natural andsynthetic rubbers are poor thermal conductors and because the operatingtime of the gas generator is very short, almost any of these rubbers canbe used to .fabricate the annular members 28, 30. The preferredmaterials are the resilient silicon rubbers which are well recognized inthe art and have been used extensively in making gaskets and the like.The annular members are attached to the ends of the grain with asuitable heatresistant adhesive. Many well-known adhesives are availablefor attaching rubber to plastics and other materials. The epoxyadhesives are a particular suitable class for this purpose.

The discussion above concerns an internal-burning grain. It should benoted that this invention is not limited to internal-burning grains butcan be effectively practiced with other grains such as combinationend-internal-burning grains or internal-end-external-burning grains. Ifit is desired to use an end-internal-burning grain, the annularinhibitor members 28, 30 are not employed thus permitting the end facesof the grain 14 to become burning surfaces. If the grain is veryaccurately manufactured so as to form a tight fit within the casing 12,or the insulator liner 26 if used, it may not be necessary to inhibitthe outer surface of the grain since flow of hot gases around the outersurface would be prohibited by the tight fit. A bsent such a tight fit,however, it would be necessary to inhibit the outer surface of the grainthrough the use of an inhibitor sleeve (not shown) made of anyconventional inhibiting materials such as polysulfides, polyepoxides,alkyne resins, etc. The inhibitor may have inorganic fibers such asglass and asbestos or organic fibers such as cord, rayon, nylon, orcombinations thereof incorporated therein as a reinforcing member. Themeans for applying the inhibitor to the grain are well-known in thepropellant and rocket art and since it does not comprise this invention,it will not be explored further.

If it is desired to have burning along all the exposed surfaces of thegrain 14, i.e., internal surface, end faces and external surface, theannular members 28, 30 are not employed and the grain is formed so as tohave a fit within the casing which permits the flow of hot gases aroundthe outer surface of the grain. When the grain is permitted to burn onits external surface it may be necessary to'insulate the internalsurface of the casing 12 through means of a liner 26 such as wasdescribed above.

The inserts 16, 18 serve to position the grain 14 in place and toprovide apertures 31, 32 through which the combustion products exhaustinto the external atmosphere contiguous to each end of the casing 12.The apertures are sized so as to provide the desired pressure within thecombustion section 13, the particular internal pressure being dictatedby the particular application of the gas generator and the particularpropellant used. For example, the pressure must be sufficiently higherthan the ambient pressure to eflfect the desired degree of fracturingand/ or cleaning. Furthermore, the propellant burning rate variesdirectly with the pressure and, therefore, the apertures 31, 32 aresized to provide the pressure required for a desired burning rate. Theapertures 31, 32 are identical in size and shape and are oriented inexactly opposed directions in order to avoid the generation of apositive resultant thrust.

The inserts 16, 18 are fixedly mounted within the easing 12 and held inplace by expandable retention means 33, 34, such as snap rings. Theretention means 33, 34 are reecived within annular grooves 36, 38provided in the outer surface of the inserts 16, 18, respectively. Anannular recess is provided in the inner surface of the casing 12adjacent each end thereof and is spaced from end so as to-eoincide withthe grooves 36, 38 of the insert when the inserts are properly locatedwithin the casing 12. The recesses are denoted as 40, 42. The inserts16, 18 are slipped into place and when they are in the proper positionthe retention means 33, 34 expand and concurrently seat within thegrooves 26, 28 and their corresponding recesses 40, 42 respectively. Theretention means lock the inserts in place and prevent their removal thusmaking the gas generator tamper entering the interior of the casing 12and in order to effect build-up of a predetermined pressure within thecasing 12 when the grain 14 is ignited, the apertures 31,

32 of the inserts 16, 18 are obturated by diaphragms 20,

22, respectively. The diaphragms, which may be in the form of metaldiscs, are fixedly mounted adjacent the exterior surface of the inserts16, 18. This is accomplished by providing annular recesses 48, 50 in theouter surface of the insents 16, 18, respectively, the recesses 48, 50communicating with the apertures 31, 32 as shown in FIGURE 1. Therecesses circumscribe the apertures such that when the diaphragms 20, 22are placed therein, the apertures 31, 32 are completely obturated. Inorder to hold the diaphragms in place, the ends of the inserts are.coldrolled causing the insert material immediately adjacent thediaphragms to flow over the peripheral surface of the diaphragms thusretaining them in place. The pressure within the casing is controlled bythe resisting strength of the diaphragms. This strength is a function ofthe diaphragm material, the diaphragm size, and the amount of insertmaterial rolled over the diaphragm periphery.

One or more conventional igniter means, 24, comprising a squib andpyrotechnic igniter, are located Within the propellant grain 14. Theigniter means 24 is supported within the grain by a plug 51 made ofinert material such as foamed polyurethane or foamed polystyrene.Igniter leads 52 are led to the exterior of the casing through anorifice 54 provided in one diaphragm 20. To avoid leakage through theorifice 54 appropriate sealing between the leads 52 and the diaphragm 20is required such as is indicated at 55.

The gas generating well-treating apparatus is operated as follows. Thegas generator 10 is lowered into the well to the desired depth at whichtime the igniter means 24 is energized by use of any conventionalelectrical source (not shown), such as an electric storage battery.Energization of the igniter means 24 causes ignition of the propellantgrain 14 which, in turn, effects generation of high temperaturecombustion products. The pressure within the casing 12 increases to apredetermined value at which time the diaphragms 20, 22 are ejected. Thecombustion gases then flow through the apertures 31, 32 and into thewell. Because the apertures 31, 32 are equal in design andcross-sectional area there will be no result-ant thrust, thus avoidingpropulsion of the gas generator 10.

A second embodiment of this invention, illustrated in FIGURE 5, employsinserts one of which is shown at 60, which are removably mounted on theends of the casing 12. One particu-alr design of such an insert is shownas having .a flanged portion 62 which abuts the end of the casing 12 andis secured to the casing 12 by any conventional attaching means such asa plurality of bolts 64. When bolts are employed, a plurality ofinternally threaded bolt holes 66 is provided through the end of thecasing 12 to receive the bolts 64. Use of removably mounted inserts 60permits reloading of the casing 12 by merely removing the gas generatorfrom the well, disassembling the inserts 60, and reloading the casingwith a new propellant grain 14 and then replacing the inserts 60 back onthe casing. It should be noted that in such a reloadable gas generator,it is necessary only to have one of the inserts removable, however, forsimplicity of manufacture and storage of parts, and for symmetry ofdesign it may be desirable to have the inserts at both ends of thecasing 12 removable.

FIGURE 6 illustrates another removable insert 68 which is secured to thecasing 12 by means of bolts 70 passing radially through the casing 12.FIGURE 6 additionally illustrates another means for fixedly mounting thediaphragm 20 to the gas generator. The diaphragm mounting isaccomplished by welding the diaphragm 20 to the casing 12, as indicatedby the weld beads 72. While the welded mounting will not providepressures within the casing as accurately and reproducibly as will themounting described above in the discussion of the first embodiment, sucha method is suflicient for welltreating apparatus where strict accuracyis not critical.

Another method of removably mounting an insert in the casing 12 isillustrated in FIGURE 7 wherein the insert 74 is held in place by aresilient snap ring 76. The snap ring 76 is received within an annulargroove 78 provided in the inner surface of the casing 12 adjacent theend thereof. The snap ring 76 protrudes radially inwardly beyond theinner surface of the casing 12 and abuts the exposed surface 80 of theinsert 74. The insert is urged rearwardly against the snap ring 78 bythe resilient annular member 28 when such a member is used or by thegrain 14 when the annular member is not employed.

Still another method of removably mounting an insert in the casing 12 isillustrated in FIGURE 8 wherein the external surface of the insert 82 isthreaded as shown at 84 and is received by the casing 12 having athreaded inner surface 86. It should be clear from the severalparticular embodiments described above and illustrated in FIGURE 1, andFIGURES 5 through 8, that many con ventional means may be employed tomount the inserts and, therefore, this invention is not limited to thosespecific means described herein.

It can be seen that the gas generating well-treating apparatus of thisinvention provides a means which is very inexpensive to manufacturesince all parts can be easily mass-produced. Furthermore, use of the gasgenerator is similarly inexpensive since all that is required inaddition to the gas generator itself is a source of electricity such asan electric storage battery. Obviously, such equipment can be easily andsafely stored and transferred from location to location. Furthermore, itis well established that solid propellants may be successfully storedover wide ranges of temperatures and pressures without detrimentaleifects, thus permitting storage of the gas generators for a long periodof time over wide climatic conditions. The gas generator is arapid-burning nonexplosive device which produces high pressure,high-flowing gas without the detrimental effects of an explosive such asnitroglycerin.

What is claimed as new and intended to be secured by Letters Patent ofthe United States is:

1. In combination with a well bore, a well-treating apparatus includinga neutral-thrust gas generator adapted to be lowered into said bore,said gas generator comprising (a) a tubular cylindrical casing having acombustion section therein,

(b) a solid propellant grain mounted within said combustion section,

(c) ignition means mounted within said combustion section to ignite saidgrain,

(d) apertured means at each end of said casing to provide flowcommunication between said combustion section and the externalatmosphere contiguous to each end of said casing, and

(e) means to obturate each of said apertured means to effect preventionof moisture from entering said casing and to effect build-up of apredetermined pressure within said combustion section, the obturationmeans being ejected upon attainment of said predetermined pressurewithin said combustion section.

2. In combination with a well bore, a well-treating apparatus includinga neutral-thrust gas generator adapted to be lowered into said bore,said gas generator comprismg (a) a tubular cylindrical casing having acombustion section therein,

(b) a solid propellant grain mounted within said combustion section,

(c) ignition means mounted within said combustion section to ignite saidgrain,

(d) an apertured insert removably mounted on each end of said casing toprovide flow communication between said combustion section and theexternal atmosphere contiguous to each end of said casing, and i (e)means to obturate said apertured insert to effect prevention of moisturefrom entering said casing and to effect build-up of a predeterminedpressure within said combustion section, the obturation means beingejected upon attainment of said predetermined pressure within saidcombustion section.

3. In combination with a well bore, a well-treating apparatus includinga neutral-thrust gas generator adapted to be lowered into said bore,said gas genera-tor 'comprising (d) ignition means mounted Within saidcombustion section to ignite said grain,

(e) an apertured insert removably mounted on each end of casing toprovide flow communication between said combustion section and theexternal atmosphere contiguous to each end of said casing,

(f) attachment means securing said aperture-d insert to said casing, and

(g) a diaphragm fixedly mounted against the outwardly exposed surface ofeach of said apertured inserts to effect prevention of moisture fromentering said casing and to effect build-up of a predetermined pressurewithin said combustion section, said diaphragm being ejected uponattainment of said predetermined pressure within said combustionsection.

4. Well-treating apparatus as defined in claim 3 Wherein said attachmentmeans includes an expandable retention means and an annular grooveprovided in the inner surface of said casing adjacent said exposedsurface of each of said inserts, said retention means residing in saidgroove and projecting radially inwardly beyond said inner surface ofsaid casing to secure said insert in said casmg.

5. In combination with a Well bore, a Well-treating apparatus includinga neutral-thrust gas generator adapted to be lowered into said bore,said gas generator comprising (a) a tubular cylindrical casing having acombustion section therein, said casing having a recess provided in theinternal surface adjacent each end thereof,

(b) an internal-burning solid propellant grain mounted Within saidcombustion section,

(c) ignition means mounted within said combustion section to ignite saidgrain,

(d) a pair of apertured inserts, one of said inserts being mounted insaid casing at each end thereof, each of said inserts having a groove inthe outer surface thereof, each of said grooves being radial-1y alignedwith one of said recesses,

(e) expandable retentionmeans for retaining each of said inserts Withinsaid casing, one of said retaining means being seated concurrentlyWithin each of said grooves and in the corresponding recess aligned withsaid each of said grooves, and

(f) means to obturate each of said apertured inserts to effectprevention of moisture from entering said casing and to effect build-upof a predetermined pressure Within said combustion section, said meansbeing ejected upon the attainment of said predetermined pressure withinsaid combustion section.

References Cited by the Examiner UNITED STATES PATENTS 2,613,497 10/1952MacDonald 6035.6 2,816,418 12/1957 Loedding 60-35.6 2,952,972 9/ 1960Kimmel et a1 10249 2,958,185 11/1960 Sanders 6035.6 3,001,584 9/1961Scott 166-63 3,044,255 7/ 1962 Precoul 102-49 3,064,423 11/1962 Frey10298 X 3,066,734 12/ 1962 Meiklejohn 16642 3,010,117 8/1963 Scott et al16667 3,171,248 3/1965 Ledwith 60-35.6

OTHER REFERENCES Amer. Rocket Society Journal, vol. 29, No. 7, July1959, Recent Advances in Solid Propellant Grain Design, pp. 483, 484required.

BENJAMIN A. BORCHELT, Primary Examiner.

R. F. STAHL, Assistant Examiner.

1. IN COMBINATION WITH A WELL BORE, A WELL-TREATING APPARATUS INCLUDINGA NEUTRAL-THRUST GAS GENERATOR ADAPTED TO BE LOWERED INTO SAID BORE,SAID GAS GENERATOR COMPRISING (A) A TUBULAR CYLINDRICAL CASING HAVING ACOMBUSTION SECTION THEREIN, (B) A SOLID PROPELLANT GRAIN MOUNTED WITHINSAID COMBUSTION SECTION, (C) IGNITION MEANS MOUNTED WITHIN SAIDCOMBUSTION SECTION TO IGNITE SAID GRAIN, (D) APERTURED MEANS AT EACH ENDOF SAID CASING TO PROVIDE FLOW COMMUNICATION BETWEEN SAID COMBUSTIONSECTION AND THE EXTERNAL ATMOSPHERE CONTIGUOUS TO EACH END OF SAIDCASING, AND (E) MEANS TO OBTURATE EACH OF SAID APERTURED MEANS TO EFFECTPREVENTION OF MOISTURE FROM ENTERING SAID CASING AND TO EFFECT BUILD-UPOF A PREDETERMINED PRESSURE WITHIN SAID COMBUSTION SECTION, THEOBTURATION MEANS BEING EJECTED UPON ATTAINMENT OF SAID PREDETERMINEDPRESSURE WITHIN SAID COMBUSTION SECTION.